Power line communication (herein abbreviated PLC) refers to methods and systems for enabling data to be transferred over electrical cables. PLC is also referred to in the art as power line digital subscriber line, power line carrier, mains communication, power line telecom and power line networking. In the case that PLC is used to provide access to the Internet, or for video distribution over a network, the methods and systems are referred to as broadband over power lines (herein abbreviated BPL). Electrical cables can also be referred to as power cables, power lines, electrical power lines, electrical wiring, electrical cabling and the like. These terms are used interchangeably herein and represent the cabling used to transfer electricity from an electricity provider, such as an electric company (e.g. Pacific Gas & Electric, Florida Power & Light, etc. . . . ) or an electricity generator (e.g., a wind energy converter), to a residence, as well as the wires used in a residence to transfer electricity to various wall sockets, electrical outlets, wall plugs and power points in the residence. PLC enables various devices, such as computers, printers, televisions and other electrical devices in a residence, to be coupled with one another, as a network, without the need for new wires to be added to the residence. A residence can refer to a private home, an apartment building, an office building or other structures where people live that receive electricity. Each device to be coupled in the network requires a separate element for enabling it to transfer data over the electrical wiring. Such an element is usually referred to as a modem, and commonly referred to in the art as a power line modem. Such modems usually transfer data in the high frequency range, which is usually on the order of megahertz or higher. PLC methods are known in the art.
US Patent Application Publication No. 2008/0057866 A1, issued to Schwager et al., entitled “Method for transmitting a signal on a power line network, transmitting unit, receiving unit and system” is directed to a system and method for transmitting a signal on a PLC network. The PLC system includes first and second diversity PLC-modems connected to a power line network, e.g. a building network. The PLC-modems use the power-line network to transmit and receive data. The power-line network includes three lines: phase (P), neutral (N) and protective earth (PE). The PLC-modems are connected to and utilize all three lines by transmitting data on pairs of the lines: P-N, N-PE or P-PE. The receiving PLC-modem includes a transmitting unit T and a receiving unit R, which is adapted to receive DM (i.e., differential mode) signals from any combination of lines. The transmission unit T includes a signal generator, a transmitter and a transmitter connector. The receiver unit R includes a receiver connector, a receiver and a combiner. The signal generator of the transmitting unit T is coupled to the transmitter. The transmitter connector connects the transmitter to all of the three network lines (P, N, PE). The receiver connector of the receiving unit R connects the receiver to all of the three network lines. The receiver is coupled to the combiner. A receiving connector may be adapted to act as a transmitting connector and vice-versa when transmitting or receiving signals in the other direction. The signal generator of the transmitting unit T receives a signal from which at least two auxiliary signals are generated. The auxiliary signals are transmitted through at least two transmission channels. The receiver of the receiving unit R receives the two auxiliary signals. The two received auxiliary signals are transmitted to the combiner, which combines the signals in order to obtain the original signal. A transmission channel may use two out of the three pairs of lines for signal feeding and all three combinations of pairs for receiving. Measurements show that different transmission channels obtain different fading characteristics for different frequency bands. Channel characteristics are evaluated by the transmitting unit T and receiving unit R of the intended transmitting and receiving PLC-modems prior to or during the transmission of the at least two auxiliary signals. According to the aforementioned evaluation, the transmission unit T determines which feeding channels are best suited for the specific transmission frequency band, which is intended to be used or in use. Evaluation of channel characteristics should be measured over time, since it may change in time. Advanced diversity techniques may be used, such as MIMO (i.e., Multiple-In Multiple-Out), thereby allowing transmission of different signals over the individual transmission links. If so, channel evaluation is performed for each individual link. Transmission channels may differ in, but are not limited to, the frequency domain, phase domain, time domain or spatial domain. Common mode signals may be detected in addition.
US Patent Application Publication No. 2009/0060060 A1, issued to Stadelmeier et al., entitled “Method for transmitting a signal from a transmitter to a receiver in a power line communication network, transmitter, receiver, power line communication modem and power line communication system” is directed to a system and method for transmitting signals in PLC networks. The PLC system includes first and second PLC modems in a MIMO mode. Each PLC modem may be used as both transmitter and receiver, thereby forming a bidirectional communication network. The PLC modems are connected to a home installation. The home installation includes three wires: phase line (P), neutral line (N) and protective earth (PE). Feeding signals are performed between a pair of the wires, hence allowing three possible transmission paths: P-N, N-PE and P-PE. The PLC modem, which is in a transmission mode, uses two transmission paths, and the PLC modem, which is in a receiving mode, uses all three possible transmission paths. In addition, a common mode (CM) path may be used. The transmitting PLC modem transmits an initial data burst, which includes a training sequence, to the receiving PLC modem. The receiving PLC modem evaluates the MIMO channels and calculates encoding and decoding matrices from the evaluated MIMO channels' eigenvalues and an adaptive OFDM tonemap. A feedback data is transmitted back to the transmitting PLC modem. The receiving PLC modem selects the adaptive OFDM tonemap for decoding and a corresponding decoding eigenbeamforming matrix. The transmitting PLC modem selects the adaptive OFDM and the encoding eigenbeamforming matrix according to the feedback data in order to build a message. The message is transmitted to the receiving PLC modem, which uses the adaptive OFDM tonemap and the decoding eigenbeamforming matrix in order to generate the original message.
US Patent Application Publication No. 2008/0273613 A1, issued to Kol, entitled “Multiple input, multiple output (MIMO) communication system over in-premises wires” is directed to a multiple channel power line communication system. The system includes a plurality of MIMO devices. The MIMO devices are PLC devices, which utilize the in-premises power line network in order to transfer data. The in-premises power-line network includes a phase line (P), a neutral line (N) and a ground line (G). Each MIMO device may include a transmitter and a receiver. The transmitter may include a MIMO transmit processor and multiple analog front-ends (AFEs). The reciever may include a MIMO receive processor and multiple analog front-ends (AFEs). Each AFE included within the transmitter or the receiver may include a digital to analog converter (DAC), an analog to digital converter (ADC) and an analog and/or digital filters, mixers and amplifiers.
Each AFE is connected to a pair of lines selected out of the phase, neutral and ground lines (i.e., P-N, N-G or P-G), where each such combination of lines forms a channel of communication. The transmit processor processes an input data stream to be transmitted. The transmit processor may generate two independent signals from a signal which is designated for transmission. The transmit processor then may transmit each independent signal by a different AFE, thereby by a different channel. AFEs within the receiver may receive the independent signals and process them. The received signals may include a contribution from the “straight path” (the channel through which they are connected) and the “cross path” (the channels through which they aren't connected). The receive processor utilizes information concerning the frequency-response of the different channels in order to reconstruct the two independent transmitted signals and to produce an output data stream. The channels may be also used to increase channel diversity by transmitting the same information through multiple channels. In this case, the transmit processor may include a space-time encoder and the receive processor may include a space-time decoder. The transceiver and receiver may each include a mode negotiator. The mode negotiator may select, with respect to each channel, between two modes: transmitting two independent signals (multiplexing) or transmitting the same signal through multiple channels (spatial diversity). The selection is made based on the measured channel characteristics and requested speed. In another embodiment, a single transceiver may communicate in a bidirectional manner with two different transceivers through two different channels, each channel including a combination of a pair of lines (P-N, N-G or P-G). Thus, two independent data streams may flow through two different channels simultaneously and use overlapping frequency bands.
An article entitled “MIMO for Inhome Power Line Communications,” to L. Stadelmeier et al., is directed to MIMO schemes for inhome applications. In many parts of the world, the inhome installation includes three wires (Phase, Neutral and Ground) leading to three differential feeding possibilities: P-N, N-G, P-G. Only two out of the three possible combinations may be used in the transmitting end and all three may be used in the receiving end. Capacity calculations are performed in private flats and houses. The capacity may be calculated as the sum of two independent SISO channels. There may be several MIMO arrangements which differ in the number of transmit and receive ports. Two basic MIMO schemes may be applied to an OFDM based PLC system. One is spatial multiplexing, in which different signals are transmitted over different transmit ports and capacity gain is achieved. The other is space-time or space-frequency encoding, in which a signal is transmitted through multiple transmit ports, thereby obtaining diversity gain and increased certainty in the signal received. Measurements show that the MIMO schemes show better performance than the existing SISO schemes and show increases in channel capacity.
An article entitled “Space-Frequency Coded OFDM Systems for Multi-Wire Power Line Communications,” to C. L. Giovaneli et al., published in the proceedings of the International Symposium on Power Line Communications and Its Applications, 2005, pages 191-195, is directed to a space-frequency coded orthogonal frequency-division multiplexing (OFDM) system for high-speed data transmission over frequency selective multi-phase power line channels. In the absence of channel knowledge at the transmitter end, frequency and space diversities are achieved by transmitting the same data symbol over two uncoupled wires and over two different carriers which are frequency-separated by carriers that are greater than the coherence bandwidth of the channels. It is assumed that channel state information is available at the receiver end. Different MIMO-OFDM techniques are known for power line channels which include four power line cables (three phase cables and neutral, e.g., access domain, large building or industrial plants). A basic multi-wire differential signaling structure used by the scheme proposed includes a transmitter and a receiver. The transmitter includes two elemental differential transmitters and a processor unit. The receiver includes two elemental differential receivers, a space-frequency (SF) linear combiner and a maximum-likelihood (ML) detector. Thus, the system utilizes two pairs of cables and forms two independent orthogonal SISO channels. The processor unit pre-codes the input data symbols prior to transmission and similarly pre-codes the orthogonal SISO-OFDM data symbols. The OFDM data symbols are transmitted serially over the two orthogonal SISO channels. The data symbols are received at each receiving point. The SF linear combiner realigns the output signals from one channel and its associated estimation with respect to the signals and estimation of the output signals of the other channel. After the realigning operation, the two signals include the same transmitted data symbol. The combiner additionally performs linear combining by using the method of maximal-ratio combining (MRC). The ML detector detects the optimal data symbol at the output of the SF linear combiner. Simulation results show that the proposed schemes perform significantly better than the conventional single-wire OFDM systems and that the symbol error rate (SER) of the proposed scheme outperforms the conventional SISO scheme when the power line channel is corrupted by impulsive noise.